The use of metallocene-based catalysts for the polymerization of olefins is well known. A variety of metallocene catalyst precursor compounds have been shown to be highly useful in the preparation of polyolefins, producing relatively homogeneous copolymers at good polymerization rates. In contrast to traditional Ziegler-Natta catalyst compositions, metallocene-based catalyst compositions contain one or only a few polymerization sites, thereby allowing one to tailor the properties of the finished polymer closely. However, relatively little is still known as to how individual structural features of metallocene catalyst precursor compounds influence the properties of the polymers produced thereby.
U.S. Pat. No. 6,034,192, fully incorporated herein by reference, discloses germanium bridged metallocenes such as, e.g., diethylgermanium cyclopentadienyl tetramethylcyclopentadienyl zirconium dichloride for the production of ethylene polymers with increased melt strength. PCT Patent Application Publication No. WO 99/41294, fully incorporated herein by reference, is directed to a solution polymerization process for the preparation of ethylene copolymers with a catalyst composition prepared from a bridged bis(cyclopentadienyl) zirconium compound having an unsubstituted cyclopentadienyl ligand and a multiply substituted cyclopentadienyl ligand. The process is stated to exhibit high catalyst activity, high comonomer incorporation and high diene monomer conversion rates and to be particularly suitable for the preparation of ethylene-based elastomers.
In addition, pending U.S. patent application, Ser. No. 09/306,142, filed May 6, 1999, U.S. Pat No. 6,339,134 incorporated herein by reference, discloses cyclic bridged metallocene catalyst systems, their use in a polymerization process, and products produced therefrom. Pending U.S. patent application, Ser. No. 09/955,507, filed Sep. 18, 2001, which is a continuation of U.S. patent application, Ser. No. 09/451,805 filed Dec. 12, 1999, both incorporated herein by reference, disclose cyclic germanium bridged metallocene catalyst systems.